Single-Shot Semiconductor Processing System and Method Having Various Irradiation Patterns

ABSTRACT

High throughput systems and processes for recrystallizing thin film semiconductors that have been deposited at low temperatures on a substrate are provided. A thin film semiconductor workpiece is irradiated with a laser beam to melt and recrystallize target areas of the surface exposed to the laser beam. The laser beam is shaped into one or more pulses. The beam pulses have suitable dimensions and orientations to pattern the laser beam radiation so that the areas targeted by the beam have dimensions and orientations that are conductive to semiconductor recrystallization. The workpiece is mechanically translated along linear paths relative to the laser beam to process the entire surface of the workpiece at high speeds. Position sensitive triggering of a laser can be used to generate laser beam pulses to melt and recrystallize semiconductor material at precise locations on the surface of the workpiece while it is translated on a motorized stage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/708307, filed Feb. 18, 2010, which is a continuation of U.S. patentapplication Ser. No. 10/524,809, filed on Feb. 15, 2005, which is anational phase of International Patent Application No. PCT/US03/02594,filed Aug. 19, 2003, published on Feb. 26, 2004 as International PatentPublication No. WO 04/017381, which claims priority from U.S.Application No. 60/404,447, which was filed on Aug. 19, 2002, each ofwhich are incorporated by reference in their entireties herein, and fromwhich priority is claimed.

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor processing methods, andmore particularly, to methods for making semiconductors materials in aform suitable for fabrication of thin-film transistor (“TFT”) devices,

Flat panel displays and other display units are used as visual imaginginterfaces for the common and ubiquitous electronic devices andappliances such as computers, image sensors, and television sets. Thedisplays are fabricated, for example, from thin films of liquid crystaland semiconductor material placed on glass or plastic substrates. Eachdisplay is composed of a grid (or matrix) of picture elements (“pixels”)in the liquid crystal layer. Thousands or millions of these pixelstogether create an image on the display. TFT devices fabricated in thesemiconductor material layer are used as switches to individually turneach pixel “on” (light) or “off” (dark). The semiconductor materialsused for making the TFTs, traditionally, are amorphous orpolycrystalline silicon thin films. These films are deposited on to thesubstrates by physical or chemical processes at relatively lowdeposition temperatures in consideration of the low melting temperaturesof the substrate materials used (e.g., glass or plastic). The relativelylow deposition temperatures degrade the crystallinity of the depositedsilicon films and cause them to be amorphous or polycrystalline.

Unfortunately, the device characteristics of a TFT fabricated in asilicon thin film undesirably degrade generally in proportion to thenon-crystallinity of the silicon thin film. For industrial TFT deviceapplications, silicon thin films of good crystalline quality aredesirable. The crystallinity of a thin film of silicon deposited at lowtemperatures on a substrate may be advantageously improved by laserannealing. Maegawa et al. U.S. Pat. No. 5,766,989, for example,describes the use of excimer laser annealing (“ELA”) to processamorphous silicon thin films deposited at low temperatures intopolycrystalline silicon thin films for LCD applications. Theconventional ELA processes, however, are not entirely satisfactory atleast in part because the grain sizes in the annealed films are notsufficiently uniform for industrial use. The non-uniformity of grainsize in the annealed films is related to the beam shape of the laserbeam, which is used in the ELA process to scan the thin film.

Im et al. U.S. Pat. No. 6,573,531 and Im U.S. Pat. No. 6,322,625(hereinafter “the '531 patent” and “the '625 patent”, respectively),both of which are incorporated by reference herein in their entireties,describe laser annealing apparatus and improved processes for makinglarge grained polycrystalline or single crystal silicon structures. Thelaser annealing processes described in these patents involve controlledresolidification of target portions of a thin film that are melted bylaser beam irradiation. The thin film may be a metal or semiconductormaterial (e.g., silicon). The fluence of a set of laser beam pulsesincident on the silicon thin film is modulated to control the extent ofmelting of a target portion of a silicon thin film. Then, between theincident laser beam pulses, the position of the target portion isshifted by slight physical translation of the subject silicon thin filmto encourage epitaxial lateral solidification. This so-called lateralsolidification process advantageously propagates the crystal structureof the initially molten target portion into grains of large size. Theapparatus used for the processing includes an excimer laser, beamfluence modulators, beam focussing optics, patterning masks, and amotorized translation stage for moving the subject thin film between orduring the laser beam irradiation. (See e.g., the '531 patent, FIG. 1,which is reproduced herein).

Consideration is now being given to ways of further improving laserannealing processes for semiconductor thin films, and in particular forrecrystallization of thin films. Attention is directed towards apparatusand process techniques, with a view to both improve the annealingprocess, and to increase apparatus throughput for use, for example, inproduction of flat panel displays.

SUMMARY OF THE INVENTION

The present invention provides systems and methods for recrystallizingamorphous or polycrystalline semiconductor thin films to improve theircrystalline quality and to thereby make them more suitable for deviceapplications. The systems and processes are designed so that largesurface area semiconductor thin films can be processed quickly.

Target areas of the semiconductor thin film may be intended for all orpart semiconductor device structures. The target area may, for example,be intended for active regions of the semiconductor devices. The targetareas are treated by laser beam irradiation to recrystallize them. Thetarget areas are exposed to a laser beam having sufficient intensity orfluence to melt semiconductor material in the target areas. A one shotlaser beam exposure may be used—the melted semiconductor materialrecrystallizes when the laser beam is turned off or moved away from thetarget area.

A large number of target areas in a region on the surface of thesemiconductor thin film may be treated simultaneously by using laserradiation that is patterned. A projection mask can be deployed tosuitably pattern the laser beam. The mask divides an incident laser beaminto a number of beamlets that are incident on a corresponding number oftarget areas in a surface region of the semiconductor thin film. Each ofthe beamlets has sufficient fluence to melt the semiconductor materialin target area on which it (beamlet) is incident. The dimensions of thebeamlets may be chosen with consideration to the desired size of thetarget areas and the amount of semiconductor material that can beeffectively recrystallized. Typical beamlet dimensions and correspondingtarget area dimensions may be of the order of the order of about 0.5 μmto a few μm.

An exemplary mask for patterning the laser beam radiation has a numberof rectangular slits that are parallel to each other. Using this mask,an incident laser beam can be divided into a number of parallelbeamlets. The target areas corresponding to these beamlets aredistributed in the surface region in a similar parallel pattern. Anotherexemplary mask has a number of rectangular slits that are disposed in arectangular pattern of sets of parallel and orthogonal slits. The slitsmay for example, be arranged in pairs along the sides of squares. Usingthis mask the resultant radiation beamlets and the corresponding targetareas also are distributed in a similar rectangular pattern (e.g., insets of parallel and orthogonal target areas).

The laser beam may be scanned or stepped across the surface of thesemiconductor thin film to successively treat all regions of the surfacewith a repeating pattern of target areas. Conversely, the semiconductorthin film can be moved relative to a laser beam of fixed orientation forthe same purpose. In one embodiment of the invention, a motorized lineartranslation stage is used to move the semiconductor thin film relativeto the laser beam in linear X-Y paths so that all surface regions of thesemiconductor thin film can be exposed to the laser beam irradiation.The movement of the stage during the process can be continuous across awidth of the semiconductor thin film or can be stepped from one regionto the next. For some device applications, the target areas in oneregion may be contiguous to target areas in the next region so thatextended strips of semiconductor material can be recrystallized. Therecrystallization contiguous target areas may benefit from sequentiallateral solidification of the molten target areas. For other deviceapplications, the target areas may be geometrically separate from targetareas in the adjoining areas.

The generation of laser beam pulses for irradiation of the target areasmay be synchronized with the movement of the linear translation stage sothat the laser beam can be incident on designated target areas withgeometric precision. The timing of the generated laser beam pulses maybe indexed to the position of the translation stage, which supports thesemiconductor thin film. The indexing may be occur in response toposition sensors that indicate in real time the position of the stage,or may be based on computed co-ordinates of a geometrical gridoverlaying the thin film semiconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature, and various advantageswill be more apparent from the following detailed description of thepreferred embodiments and the accompanying drawings, wherein likereference characters represent like elements throughout, and in which:

FIG. 1 is a schematic and block diagram of a semiconductor processingsystem for the laser annealing of semiconductor thin films forrecrystallization;

FIG. 2 is a top exploded view of an exemplary thin film workpiece;

FIGS. 3 a and 3 b are top views of exemplary masks in accordance withthe principles of present invention;

FIG. 4 is a schematic diagram illustrating a portion of the thin filmsilicon workpiece of FIG. 2 that has been processed using the mask ofFIG. 3 a, in accordance with the principles present invention;

FIG. 5 is a schematic diagram illustrating an exemplary processed thinfilm silicon workpiece that has been processed using the mask of FIG. 3b in accordance with the principles present invention; and

FIG. 6 is a schematic diagram illustrating an exemplary geometricalpattern whose co-ordinates are used to trigger radiation pulses incidenton a silicon thin film workpiece in accordance with the principlespresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides processes and systems forrecrystallization of semiconductor thin films by laser annealing. Theprocesses for recrystallization of semiconductor thin films involveone-shot irradiation of regions of a semiconductor thin film workpieceto a laser beam. The systems direct a laser beam to a region or spot onthe surface of the semiconductor thin film. The incident laser beam hassufficient intensity or fluence to melt targeted portions of the regionor spot of the semiconductor thin film on which the laser beam isincident. After the targeted incident areas or portions are melted, thelaser beam is moved or stepped to another region or spot on thesemiconductor thin film. The molten semiconductor materialrecrystallizes when the incident laser beam is moved away. The dwelltime of the laser beam on a spot on the semiconductor thin film may besufficient small so that the recrystallization of an entiresemiconductor thin film workpiece can be carried out quickly with highthroughput rates.

In order that the invention herein described can be fully understood thesubsequent description is set forth in the context of laser annealing ofsilicon thin films. The annealed silicon thin films may be intended furexemplary TFT device applications. It will, however, be understood thatthe invention is equally applicable to other types of materials and/orother types of device applications.

An embodiment of the present invention is described herein withreference to FIGS. 1-6. Thin film silicon workpieces (see e.g.,workpiece 170, FIGS. 2 and 4-6) are used herein as illustrativeworkpieces. Workpiece 170 may, for example, be a film of amorphous orrandomly expanding and collimating lenses 141 and 142, homogenizer 144,condenser lens 145, a field lens 148, eye piece 161, controllableshutter 152, multi-element objective lens 163), also may, for example,be any suitable commercially available optical components sold by the byLambda. Physik USA, or by other vendors.

The suitable optical components 120-163 for shaping and directing theradiation beam may include a masking system 150. Masking system 150 maybe a projection masking system, which is used for patterning incidentradiation (149) so that radiation beam (164) that is ultimately incidenton workpiece 170 is geometrically shaped or patterned.

Stage assembly 180, on which workpiece 170 rests during processing, maybe any suitable motorized translation stage capable of movement in oneor more dimensions. A translation stage capable of high translationspeeds may be advantageous for the high throughput single-shotprocessing described herein. Stage assembly 80 may be supported onsuitable support structures to isolate the thin film silicon workpiece170 from vibrations. The support structures may, for example, includeconventional optical benches such as a granite block optical bench 190mounted on a vibration isolation and self-leveling system 191, 192, 193and 194.

A computer 100 may be linked to laser 110, modulator 120, stage assembly180 and other controllable components of apparatus 1000. Computer 100may be used to control the timing and fluence of the incident laser beampulses and the relative movement of the stage assembly 180. Computer 100may be programmed to controllably move stage assembly translation stage180 in X, Y and Z directions. Workpiece 170 may be moved, for example,over predetermined distances in the X-Y plane and as well as in the Zdirection in response to instruction from computer 1000. In operation,the position of workpiece 170 relative to the incident radiation beam164 may be continuously adjusted or intermittently reset during thesingle-shot laser annealing process at suitable times according topreprogrammed process recipes for single shot recrystallization ofworkpiece 170. The movement of workpiece 170 may be synchronized orco-ordinated with the timing of radiation beam pulses generated by laser100.

In apparatus 1000, the movement of stage assembly 180 translates theworkpiece 170 and the radiation beam (164) relative to each other. Inthe processing described herein the radiation beam (164) is held fixedin a position or orientation while stage 180 is moved. Alternativeconfigurations or arrangements of optical components may be used to moveincident radiation beam 164 and workpiece 170 relative to each otheralong defined paths. For example, a computer-controlled beam steeringmirror may be used to deflect radiation beam 164 while stage 180 is heldfixed in position. By such beam deflecting arrangements it may bepossible to completely or partially dispense with the use of mechanicalprojection masks (e.g., masking system 150) and instead use electronicor optical beam guiding mechanisms to scan or step selected portions ofworkpiece 170 at a rapid pace.

Using apparatus 1000, sequential lateral solidification of moltensemiconductor material may be achieved using, for example, the processesthat involve incremental movement or shifting the position of stage 180between excimer laser pulses as described in the '531 patent. Themovements of stage 170 are small, so that the portions of the siliconthin film that are molten by sequential pulses are proximate to eachother. The proximity of the two molten portions allows the first portionto recrystallize and propagate its crystal structure into the adjacentportion, which is melted by the next puke.

In the single shot recrystallization processes described here, apparatus1000 may be used to scan or step a laser beam across the surface of asemiconductor thin film by moving of stage assembly 180. The laser beamhas sufficient intensity or fluence to melt target areas in the regionsor spots at which the laser beam pulses are incident. To process anentire workpiece 170, stage assembly 180 may be moved predetermineddistances to cause the laser beam to move along paths acrosssemiconductor thin film 175/workpiece 170. FIG. 2 also schematicallyshows paths 230, 255 etc. that may be traced by incident radiation beam164 as it is moved across the surface of the workpiece 170.

The number of paths and their geometrical orientation may be determinedby the cross sectional dimensions of the laser beam and the target arearequirements of the circuit or device applications for which workpiece170 is being processed. Accordingly, the surface of a semiconductor thinfilm 175/workpiece 170 may be partitioned in a geometric array ofregions for generating processing recipes for computer 1000 or otherwisecontrolling the operation of apparatus 1000. FIG. 2 shows an exemplarygeometrical partitioning of the surface of a semiconductor thin film 175on workpiece 170. In the exemplary geometrical partitioning shown inFIG. 2, the surface is divided into a number of rows (e.g., 205, 206,207, etc.) each having a width W. The widths of rows W may be selectedwith consideration to the cross sectional width of incident radiationbeam 164. Each row contains one or more regions. As an illustrativenumerical example, workpiece 170 may have x and y dimensions of about 30cms and 40 cms, respectively. Each of rows 205, 206, 207, . . . etc.,may, for example, have a width W of about Vi cm in the Y direction. Thisvalue of W may, for example, correspond a laser beam width of about thesame size. Thus, the surface of workpiece 170 can be divided into eighty(80) rows each with a length of about 30 cms in the X direction. Eachrow contains one or more regions whose combined length equals 30 cms(not shown).

The co-ordinates of each row may be stored in computer 100 for use bythe processing recipes. Computer 1000 may use the stored co-ordinates,for example, to compute the direction, timing and travel distances ofstage 180 during the processing. The co-ordinates also may be used, forexample, to time the firing of laser 110 so that designated regions ofsemiconductor thin film 175 are irradiated as stage 180 is moved.

Workpiece 170 may be translated in linear directions while silicon thinfilm 175 is being irradiated so that a linear strip of silicon thin film175 is exposed to radiation beams of melting intensity or fluence. Thetranslation paths traced by the radiation beams may be configured anthat the desired portions of the entire surface of thin film silicon 175are successively treated by exposure to laser beams. The translationpaths may be configured, for example, so that the laser beam traversesrows 205. 206, 207, etc. sequentially. In FIG. 2, the radiation beam isinitially directed to a point 220 off side 210′ near the left end of row205. Path 230 represents, for example, the translation path traced bythe center of the radiation beam through row 205 as stage 180 is movedin the negative X direction.

The movement of stage 180 may be conducted in a series of steps in anintermittent stop-and-go fashion, or continuously without pause untilthe center of the radiation beam is directed to a point 240 near theright end of row 205. Path segments 225 and 235 represent extensions ofpath 230 that may extend beyond edges 210′ and 210″ of workpiece 170 topoints 220 and 240, respectively. These segments may be necessary toaccommodate acceleration and deceleration of stage assembly 180 at theends of path 230 and/or may be useful for reinitializing stage 180position for moving stage 180 in another direction. Stage 180 may, forexample, be moved in the negative Y direction from point 240, so thatthe center of the radiation beam traces path 245 to point 247 next tothe right end of row 206 in preparation for treating the siliconmaterial in row 206. From point 247 in manner similar to the movementalong path 230 in row 205 (but in the opposite direction), stage 180 ismoved in the X direction so that the center of the radiation beam movesalong path 255 irradiating thin film silicon material in row 206. Themovement may be continued till the center of radiation beam is incidentat spot 265 that is near the left end of row 206. Path extensions 260and 250 represent segments of path 255 that may extend beyond edges 210′and 210″ to spots 247 and 265, respectively. Further linear movement ofstage 180 in the Y direction moves the center of the incident radiationbeam along path 270 to a point 272 next to row 207. Then, the thin filmsilicon material in row 207 may be processed by moving stage 180 in thenegative X direction along path 275 and further toward the opposite side210″of workpiece 170. By continuing X and Y direction movements of stage180 in the manner described for rows 205, 206, and 207, all of the rowson the surface of thin film silicon 175 may be treated or irradiated. Itwill be understood that the particular directions or sequence of pathsdescribed above are used only for purposes of illustration, otherdirections or sequences may be used as appropriate.

In an operation of apparatus 1000, silicon thin film 175 may beirradiated by beam pulse 164 whose geometrical profile is defined bymasking system 150. Masking system 150 may include suitable projectionmasks for this purpose. Masking system 150 may cause a single incidentradiation beam (e.g., beam 149) incident on it to dissemble into aplurality of beamlets in a geometrical pattern. The beamlets irradiate acorresponding geometrical pattern of target areas in a region on thethin film silicon workpiece. The intensity of each of the beamlets maybe chosen to be sufficient to induce complete melting of irradiated thinfilm silicon portions throughout their (film) thickness.

The projection masks may be made of suitable materials that blockpassage of radiation through undesired cross sectional areas of beam 149but allow passage through desired areas. An exemplary projection maskmay have a blocking/unblocking pattern of rectangular stripes or othersuitable geometrical shapes which may be arranged in random or ingeometrical patterns. The stripes may, for example, be placed in aparallel pattern as shown in FIG. 3 a, or in a mixed parallel andorthogonal pattern as shown in FIG. 3 b, or any other suitable pattern.

With reference to FIG. 3 a, exemplary mask 300A includes beam-blockingportions 310 which has a number of open or transparent slits 301, 302,303, etc. Beam-blocking portions 310 prevent passage of incidentportions of incident beam 149 through mask 300A. In contrast, open ortransparent slits 301, 302, 303, etc. permit passage of incidentportions of radiation beam 149 through mask 300. Accordingly, radiationbeam 164 exiting mask 300 A has a cross section with a geometricalpattern corresponding to the parallel pattern of the plurality of openor transparent slits 301, 302, 303, etc. Thus when positioned in maskingsystem 150, mask 300A may be used to pattern radiation beam 164 that isincident on semiconductor thin film 175 as a collection of parallelrectangular-shaped beamlets. The beamlets irradiate a correspondingpattern of rectangular target areas in a region on the surface of the onsemiconductor thin film 175. The beamlet dimensions may be selected witha view to promote recrystallization or lateral solidification of thinfilm silicon areas melted by a beamlet. For example, a side length of abeamlet may be chosen so that corresponding target areas in adjoiningregions are contiguous. The size of the beamlets and the inter beamletseparation distances may be selected by suitable choke of the size andseparation of transparent slits 301, 302, 303, etc. Open or transparentslits 301, 302, 303, etc. having linear dimensions of the order of amicron or larger may, for example, generate laser radiation beamletshaving dimensions that are suitable fir recrystallization processing ofsilicon thin films in many instances.

FIG. 3 b shows another exemplary mask 300B with a pattern which isdifferent than that of mask 300A. In mask 300B, a number of open ortransparent slits 351, 352, 361, 362. etc. may, for example, be arrangedin pairs along the sides of squares. This mask 300B also may be used inmasking system 150 to pattern the radiation beam 164 that is incident onsemiconductor thin film 175. The radiation beam 164 may be patterned,for example, as a collection of beamlets arranged in square-shapedpatterns. The beamlet dimensions may be selected with a view to promoterecrystallization or lateral solidification of thin film silicon areasmelted by a beamlet. Open or transparent slits 351, 352, 361, 362, etc.having linear dimensions of about 0.5 micron may generate laserradiation beamlets of suitable dimensions for recrystallization of thinfilm silicon areas

It will be understood that the specific mask patterns shown in FIGS. 3 aand 3 b are exemplary. Any other suitable mask patterns may be usedincluding, for example, the chevron shaped patterns described in the'625 patent. A particular mask pattern may be chosen in consideration ofthe desired placement of TFTs or other circuit or device elements in thesemiconductor product for which the recrystallized thin film siliconmaterial is intended.

FIG. 4 shows, for example, portions of workpiece 170 that has beenprocessed using mask 300A of FIG. 3 a. (Mask 300A may be rotated byabout 90 degrees from the orientation shown in FIG. 3 a). The portionshown corresponds to a row, for example, row 205 of workpiece 170 (FIG.2). Row 205 of processed workpiece 170 includes recrystallizedpolycrystalline silicon linear regions or strips 401, 402, etc. Each ofthe linear strips is a result of irradiation by a radiation beamletformed by a corresponding mask slit 301, 302, etc. The continuous extentof recrystallized silicon in the linear strips across row 205 may be aconsequence, for example, of a continuous movement of the stage 180along path 230 under laser beam exposure (FIG. 2). Strips 401, 402, mayhave a microstructure corresponding to the one shot exposure withcolliding liquid/solid growth fronts in the center creating a longlocation-controlled grain boundary. Alternatively, in a directionalsolidification process the continuous extent may be a result of closelyspaced stepped movements of stage 180 along path 230 that aresufficiently overlapping to permit formation of a continuousrecrystallized silicon strip, hi this alternative process, themicrostructure of the recrystallized material may have long grainsparallel to the scanning direction. The recrystallized polycrystallinesilicon (e.g. strips 401, 402, etc.) may have a generally uniformstructure, which may be suitable for placement of the active region ofone or more TFT devices. Similarly, FIG. 5 shows, exemplary resultsusing mask 300B of FIG. 3 b, Exemplary processed workpiece 170 includesrecrystallized polycrystalline silicon strips 501, 502, etc.Recrystallized polycrystalline silicon strips 501, 502, etc. like strips401 and 402 may have a uniform crystalline structure, which is suitablefor placement of the active regions of TFT devices. Strips 501 and 502that are shown to be generally at right angles to each other maycorrespond to radiation beamlets formed by orthogonal mask slits (e.g.,FIG. 3 b slits 351, 361). The distinct geometrical orientation andphysical separation of strips 501 and 502 (in contrast to extendedlength of strips 401 and 402) may be a consequence, for example, ofphysically separated exposure to laser radiation during the processingof workpiece 170. The separated radiation exposure may be achieved bystepped movement of stage 180 (e.g., along path 230 FIG. 2) during theprocessing. Additionally or alternatively, the separated exposure may beachieved by triggering laser 110 to generate radiation pulses atappropriate times and positions of stage 180 along path 230 while stage180 and laser beam 164 are moved or scanned relative to each other atconstant speeds.

Computer 100 may be used control the triggering of laser 110 atappropriate times and positions during the movement of stage 180.Computer 100 may act according to preprogrammed processing recipes that,for example, include geometrical design information for aworkpiece-in-process. FIG. 6 shows an exemplary design pattern 600 thatmay be used by computer 1000 to trigger laser 110 at appropriate times.Pattern 600 may be a geometrical grid covering thin film silicon175/workpiece 170. The grid may, for example, be a rectangular x-y gridhaving co-ordinates (x1, x2, . . . etc.) and (y1, y2, . . . etc.). Thegrid spacings may be regular or irregular by design. Pattern 600 may belaid out as physical fiducial marks (e.g., on the thin film workpiece)or may be a mathematical construct in the processing recipes. Computer100 may trigger laser 110 when stage 180 is at the grid coordinates (xi,yi). Computer 100 may do so in response, for example, to conventionalposition sensors or indicators, which may be deployed to sense theposition of stage 180. Alternatively, computer 100 may trigger laser 110at computed times, which are computed from parameters such as an initialstage position, and the speeds and direction of stage movements from theinitial stage position. Computer 100 also may be used advantageously toinstruct laser 110 to emit radiation pulses at a variable rate, ratherthan at a usual even rate. The variable rate of pulse generation may beused beneficially to accommodate changes in the speed of stage 180, forexample, as it accelerates or decelerates at the ends of paths 230 andthe like.

It will be understood that the foregoing is only illustrative of theprinciples of the invention and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention, which is limited only by the claims that follow.

What is claimed is: 1-20. (canceled)
 21. A method for forming anelectronic device on a semiconductor thin film, comprising: (a)providing the semiconductor thin film having a surface; (b) generating aradiation beam, wherein the beam is incident on a target area of a firstregion of the semiconductor thin film; (c) irradiating the first regionof the semiconductor thin film with a pulse of the radiation beam,wherein the radiation beam pulse has a fluence sufficient to partiallymelt the semiconductor material in the target area on which it isincident, and wherein the partially molten semiconductor material in thetarget area recrystallizes when it is no longer exposed to the incidencebeam; (d) continuously translating the semiconductor thin film relativeto the radiation beam such that a second region of the surface of thesemiconductor thin film is irradiated with a second radiation beam pulsehaving a fluence sufficient to partially melt the semiconductor materialin the second region on which it is incident, and wherein the partiallymolten semiconductor material in the second region recrystallizes whenit is no longer exposed to the incidence beam; wherein the second regioncorresponds to a second area which is adjacent to a first areacorresponding to the first region; and (e) forming the electronic devicein the target area.
 22. The method of claim 21, further the step ofcomprising supporting the semiconductor thin film on a movable stage,and wherein translating the semiconductor thin film relative to theradiation beam comprises moving the movable stage along a linear path tothe next region.
 23. The method of claim 22, wherein the semiconductorthin film comprises rows of regions, further comprising moving themovable stage along the linear path through a first row of regions onthe surface of the semiconductor thin film.
 24. The method of claim 23,wherein the movable stage is moved continuously without pause throughthe row of regions.
 25. The method of claim 24, wherein the movablestage is paused at a region and is then stepped to an adjacent region.26. The method of claim 25, further comprising moving the movable stagealong linear paths through successive rows of regions until the entiresurface of the semiconductor thin film has been processed.
 27. Themethod of claim 21, further comprising using a laser to generate a pulseof a radiation beam.
 28. The method of claim 27, wherein the lasercomprises an excimer laser.
 29. The method of claim 27, wherein thelaser is triggered to generate the pulse of the radiation beam accordingto a position of the thin film semiconductor region relative to theradiation beam.
 30. The method of claim 29, further comprisingsupporting the semiconductor thin film on a movable stage, and whereintranslating the semiconductor thin film relative to the radiation beamcomprises moving the movable stage, and wherein the laser is triggeredto generate the pulse of the radiation beam according to a position ofthe movable stage.
 31. The method of claim 30, wherein the position ofthe movable stage is sensed by position sensors.
 32. The method of claim31, wherein the position of the movable stage is computed from aninitial position of the stage.
 33. The method of claim 31, whereinforming the electronic device comprises forming a thin-film transistordevice.
 34. The method of claim 31, wherein forming the electronicdevice on at least the target area comprises forming an active channelregion of a thin-film transistor device on the target area.
 35. Themethod of claim 34, wherein forming the electronic device furthercomprises forming at least a gate electrode, a drain electrode, and asource electrode adjacent to the active channel region.
 36. A system forrecrystallizing a semiconductor thin film using a controllable radiationbeam source, comprising: a processing arrangement adapted to operativelycouple to the radiation beam source, wherein the processing arrangementis configured to: (a) control the radiation beam source to emit at leastone beam pulse, (b) irradiate a target area of a first region of thesemiconductor thin film with a pulse of the at least one beam, whereineach beam pulse has sufficient fluence to melt semiconductor material inthe target area on which it is incident, and wherein the moltensemiconductor material in the target area recrystallizes when it is nolonger exposed to the incident beam pulse; and (c) continuouslytranslate the semiconductor thin film relative to the at least one beampulse such that a second region of the surface of the semiconductor thinfilm is irradiated in the same manner as in (b), wherein the secondregion corresponds to a second area which is adjacent to a first areacorresponding to the first region.
 37. The system of claim 36, furthercomprising a movable stage and wherein the processing arrangement isfurther configured to continuously translate the semiconductor thin filmrelative to the radiation beam by moving the movable stage along alinear path.
 38. The system of claim 36, wherein at least one of thetarget areas in the first region is contiguous with at least one of thetarget areas in the second region, so that after irradiation of thefirst and second regions an extended strip of recrystallizedsemiconductor material is formed.
 39. The system of claim 36, whereinthe radiation beam source comprises a laser beam source.
 40. The systemof claim 39, wherein the laser beam source comprises a excimer laser.41. The system of claim 36, further comprising a homogenizer.